U.S. patent number 4,093,820 [Application Number 05/814,748] was granted by the patent office on 1978-06-06 for electronic echo generation equipment.
This patent grant is currently assigned to Nihon Hammond Kabushiki Kaisha. Invention is credited to Kazuo Masaki, Masashi Shibahara, Shigeru Yamashita.
United States Patent |
4,093,820 |
Yamashita , et al. |
June 6, 1978 |
Electronic echo generation equipment
Abstract
An electronic sound generation system wherein an input signal is
frequency modulated, and the modulated signal passes through a
series of cascaded shift registers. Amplifiers are provided for
compensation of insertion loss in each shift register stage, and a
frequency modulation detector is utilized to produce the
time-delayed output echo signal.
Inventors: |
Yamashita; Shigeru (Takatsuki,
JA), Masaki; Kazuo (Osaka, JA), Shibahara;
Masashi (Kishiwada, JA) |
Assignee: |
Nihon Hammond Kabushiki Kaisha
(Osaka, JA)
|
Family
ID: |
13853027 |
Appl.
No.: |
05/814,748 |
Filed: |
July 11, 1977 |
Foreign Application Priority Data
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|
|
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Jul 16, 1976 [JA] |
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51-085240 |
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Current U.S.
Class: |
381/63; 333/138;
333/165; 367/87; 377/54; 84/DIG.26 |
Current CPC
Class: |
G10K
15/12 (20130101); Y10S 84/26 (20130101) |
Current International
Class: |
G10K
15/12 (20060101); G10K 15/08 (20060101); H04R
003/00 (); H03H 007/30 () |
Field of
Search: |
;179/1J,1P ;328/55
;307/221C,221D ;333/29,23,3R ;343/17.2PC ;84/DIG.26,1.25 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; Thomas W.
Assistant Examiner: Kemeny; E. S.
Attorney, Agent or Firm: McArdle, Jr.; John J.
Claims
what is claimed is:
1. An electronic echo sound generation system having a direct path
and a delay path, the delay path comprising:
frequency modulation means for frequency modulating an input audio
signal on a carrier and having an output;
a plurality of analog shift registers operable to time delay the
modulated signal, coupled in series at a first end from the output
of the frequency modulation means;
amplifier means coupled in series with the analog shift registers
for compensating for the insertion losses of the analog shift
registers; and
frequency modulation detector means coupled from the second end of
the series coupled analog shift registers for producing at an
output an echo audio signal derived from the input audio
signal.
2. The system of claim 1 in which said amplifier means comprises an
insertion loss compensation amplifier coupled between each pair of
intercoupled analog shift registers of the plurality of analog
shift registers.
3. The system of claim 1 in which the frequency modulation means
comprises a serrasoid modulator.
4. The system of claim 3 in which the amplifier means comprises a
limiter and a filter.
5. The system of claim 2 in which the frequency modulation means
comprises a serrasoid modulator and in which each said insertion
loss compensation amplifier includes a limiter and a filter.
Description
The invention is in the field of audio signal time delay
systems.
More precisely, the presently described embodiment of the invention
relates to a system for generating electronic echo sounds which is
adapted to produce a sound of three-dimensional effect by
sequentially electronically delaying a music sound signal of
electronic or electric musical instruments and thereby converting
the signal into an echo sound.
In the figures:
FIG. 1 is a block diagram of a basic prior art echo generation
delay path system.
FIG. 2 shows a slightly improved version of the FIG. 1 system.
FIG. 3 is a block diagram of the basic structure of the presently
disclosed embodiment of the inventive echo generation system delay
path.
FIG. 4 is a more detailed block diagram of the system of FIG.
3.
It is generally known that delay elements are useful in providing
systems of the type which produce echo sounds. Various delay
elements are available, such as an element of the charge transfer
type by which an input signal is transferred with use of a clock
signal to delay the signal. This type of element is often referred
to as a bucket brigade device (BBD) or an analog shift register.
Because of its nature, the delay element, when incorporated into a
circuit, will involve an insertion loss, so that if a multiplicity
of such elements are used in cascade connection to prolong the
delay time, the circuit has the drawback which shall be described
below in regard to FIG. 1.
The input signal fed to an input terminal P1 is applied to an input
amplifier 1 in which the signal is amplified to an operation level
most suitable for charge transfer type elements, or analog shift
registers, 2 subsequent to the amplifier 1. The first analog shift
register 2a gives a specified delay time t to the signal, and the
signal is then fed to the second element 2b. However, due to the
insertion loss involved in the first element 2a, the level of the
signal applied to the second element 2b is now lower by an amount
corresponding to the insertion loss and is not at the optimum
operation level. Thus, the signal level further progressively
lowers from element to element. Consequently, if a multiplicity of
the charge transfer type elements are used in cascade connection,
the great overall insertion loss of all the elements will result in
a signal level much lower than the optimum operation level,
possibly rendering the signal no longer usuable. Even if usable,
the signal will then involve a poor signal to noise ratio and, when
amplified by an amplifier 3, will give at an output terminal P2 an
echo sound of poor quality.
In order to provide a desired prolonged delay time in the same
manner as above but free of the drawback described, it would appear
to be useful to dispose amplifiers 14 (FIG. 2) for compensating for
the insertion loss of each shift register 12, the respective
amplifier being connected to the output of each of the charge
transfer type elements, or shift registers, which are arranged in
cascade connection. In this case, the output signal fed to an input
terminal P3 is amplified by an input amplifier 11 to a level
optimum for the operation of the elements 12 and is then applied to
the first element 12a of the charge transfer type in which it is
given a predetermined delay time t.
The insertion loss occurring in the first element l2a is
compensated for by the compensation amplifier 14a, which is
connected to the element 12a and which amplifies the signal to a
degree corresponding to the insertion loss, whereupon the signal is
impressed on the second element 12b. Even in this case, however,
the noise produced in the first element 12a and in the compensation
amplifier 14a is amplified and then fed to the following element
12b, with the result that with an increase in the number of the
elements 12 used, the noise increases due to the addition of the
noise occurring in each combination of the element 12 and the
amplifier 14. Accordingly, despite the compensation of the
insertion loss, the signal will have a reduced quality and
deteriorated signal to noise ratio, and the echo sound appearing at
output terminal P4 through amplifier 13 is in need of
improvement.
The presently disclosed embodiment of the invention provides a
system for generating electronic echo sounds effectively free of
the foregoing drawbacks by delaying an input signal, the system
being adapted to use the input signal in the form of a
frequency-modulated wave amenable to noise suppression and a
carrier signal for the frequency-modulated input wave. The basic
structure of the present system is described below with reference
to FIG. 3.
FIG 3 shows an input terminal P5, an amplifier 21 for amplifying an
input signal to a modulation level, a frequency modulator 25, a
carrier oscillator 26, and a multiplicity of elements 22 of the
charge transfer, or analog shift register, type arranged in cascade
connection, with compensation amplifiers 24 interposed
therebetween. The compensation amplifiers are operative to
compensate for the insertion losses involved in the charge
transfer-type elements 22. Indicated at 27 is an FM detector, and
at 28 a clock oscillator connected to the elements 22 and adapted
to transfer the input signal. At 23, there is shown an amplifier
and at P6 the output terminal.
The input signal impressed on the input terminal P5 is amplified to
a proper modulation level by the amplifier 21 and modulated by the
carrier oscillator 26 and frequency modulator 25. The frequency
modulated signal is fed to the first element 22a of the charge
transfer type. Since the signal is a frequency-modulated wave, the
signal can be set an at optimum operation level within the dynamic
range determined by the element 22a. The insertion loss occurring
in the first element 22a is compensated for by the compensation
amplifier 24a, and the resulting signal is fed to the second
element 22b. In this way, the signal is passed through the elements
22c through 22n in cascade connection, whereby the signal is given
a specified delay time. The modulated signal is then applied to the
frequency modulation detector 27 and amplified to an output level
by the amplifier 23. The signal is thereafter emitted from the
output terminal P6 as converted to an echo sound.
A more detailed showing of the embodiment of the invention is
described below with reference to FIG. 4.
An input signal applied to an input terminal P7 is amplified by a
preamplifier 31 to a suitable modulation level for serrasoid
modulation, improved in signal to noise ratio by pre-emphasis means
39 and then fed to a frequency modulator 35 comprising a serrasoid
modulator 41, a slicer 42, a monostable multivibrator 43, and a
band pass filter 44.
The signal from the pre-emphasis means 39 is converted by the
serrasoid modulator 41 to a serrasoid-modulated wave, which is
passed through the slicer 42 and the monostable multivibrator 43
and is thereby converted to a pulse-width modulated wave (PWM). The
modulated wave is further converted by the band pass filter 44 to a
frequency-modulated wave.
The output of frequency modulator 35 is fed to an element 32a of
the charge transfer type.
The output squave wave from base oscillator 46 is frequency-divided
by 8 by frequency dividers 38, 38a and 38b, and the resulting
square wave is fed to a carrier oscillator 36, giving a sawtooth
wave which is used as a carrier signal.
The signal input to the element 32a is transferred with the clock
frequency of the frequency divider 38. The noise generated in the
element 32a is eliminated by the limiter and band pass filter of an
amplifier 34a for the compensation of insertion loss. The signal
subsequently is fed to the next element 32b of the charge transfer,
or analog shift register, type 32 and is further delayed by the
element 32b and coupled to the following compensation amplifier
34b. In this way, the signal is given a delay time t which is
dependent upon the clock frequency applied to the elements 32 from
divider 38 and the transfer factor, the combination of the
plurality of elements 32 thus giving the specified delay time.
The above embodiment resorts to serrasoid modulation which is
excellent in characteristics such as signal to noise ratio,
distortion factor, dynamic range, etc., but which however is
somewhat disadvantageous in respect to modulation angle.
Accordingly, the signal passing through the multiplicity of
elements 32a through 32n in cascade connection is fed to a
multiplier in which it is multiplied by nine to ensure satisfactory
modulation index. However, the noise involved in the modulation
step will be similarly multiplied by nine. Therefore, the output
from the multiplier and the output of the base oscillator, as
converted to a sine wave by being passed through a tank circuit 47,
are applied to a mixer 48 and thereby beaten down.
The output of the mixer 48 is impressed upon a detector 37 by way
of a limiter 49 for stabilizing the operation of the detector 37.
The output of the detector 37 is passed through a low pass filter
51 for attenuating unnecessary signals and is thereafter fed to an
equalizer 52 for the reverse compensation of the pre-emphasis. The
output of equalizer 52 is amplified by an output amplifier 33 and
emitted from an output terminal P8 as an echo sound.
The output from the detector 37 is relatively noisefree in that the
noise produced in the modulation step has been beaten down in the
mixer and limited by the limiter. Filter 51, of course, eliminates
noise outside its pass band and fully attenuates the carrier (30
khz), giving a signal having a high signal to noise ratio. The
multiplication by nine also ensures a satisfactory modulation
index, affording a fully improved signal to noise ratio.
A delay time change-over switch S is shiftable to a desired
position for delay time setting to give a desired delay time.
Although the system of this embodiment of the invention includes a
multiplicity of charge transfer type elements which are arranged in
cascade connection, the noise produced in the signal circuit does
not degrade the signal fed to the input terminal, but the frequency
modulation noise occurring in the signal path only is detected as a
noise after the detection. Consequently, the present system gives a
greatly improved signal to noise ratio as compared with the
conventional systems, effectively generating echo sounds.
* * * * *